1. Field of the Invention
The invention relates to a method of manufacturing an optical waveguide and, more particularly, to a method wherein a mother preform having a core and cladding is first formed as a rod, after which a sleeving tube is shrunk onto the mother preform and the composite preform is drawn into an optical waveguide.
2. Description of the Prior Art
Various processes of this type are known, e.g. from German Patent DE-A1 33 15 156. A problem in fusing a sleeving tube onto a mother preform consists in making sure that the core of the mother preform is located as exactly as possible in the center of the composite preform formed by fusion of the sleeving tube, i.e., that the core shows the minimum possible eccentricity with respect to the composite preform. This is because an excessively large core eccentricity in the composite preform is reproduced in the optical waveguide to be drawn from the composite preform and the waveguide will not meet the geometric requirements. The core eccentricity in optical waveguides must be small because, otherwise, an excessively high attenuation occurs at splice points and in optical waveguide connectors.
Heretofore, a mother preform was put into a sleeving tube, and the only requirement on the inner diameter of the sleeving tube was that the mother preform fit into the sleeve. In the case of a vacuum sleeving process, the gap between the mother preform and the sleeving tube causes the sleeving tube to fall down onto the preform slowly or quickly. However, a quick shrinking can cause the sleeving tube to fold, causing an unacceptable eccentricity.